Rotary valves, commonly referred to as “butterfly” valves, are typically provided with a disc which is rotationally drivable between an open position and a closed position about a central axis diametrically extending through the interior of a generally annular valve body. In the open position, the disc permits fluid flow through the valve body. Upon rotation of the disc to the closed position, a peripheral edge of the disc operatively engages an annular seal member portion of an annular seal cartridge structure supported within the valve body, to prevent fluid flow through the valve and associated piping sections.
Rotary valves are often utilized in applications requiring “bi-mode” operations, i.e. where the valve is either open or closed, such as a safety shut-off valve that generally remains open but must close, and disable the flow, during an emergency condition, such as a fire or chemical spill. Another application of rotary valve usage is throttling which regulates the amount of fluid flow per unit of time in a process. Pharmaceutical manufacturing processes, by way of example, typically incorporate throttling rotary valves to deliver precise quantities of the chemical components constituent to a product batch. A sophisticated process control system, such as the pharmaceutical process described above, may further control the throttling rotary valve to regulate the fluid flow in a time varying or cyclical manner. Applications such as these often result in the disc and the seal member remaining in constant sliding contact in relation to one another throughout the control process resulting in increased wear on both components.
While the use and operation of rotary valves in fluid throttling and shut-off applications is well known in the art, the valves are still subject to several well-known problems, limitations, and disadvantages. FIGS. 9 and 10 illustrate a prior art circular disc or circular seal rotary valve, wherein a portion of the circular valve seal along the rotational axis of the valve stem is continually in contact with a portion of the circular disc adjacent to the valve shaft resulting in continuous wear on the valve seal adjacent to the valve shaft. FIG. 9 illustrates a prior art circular rotary valve 206 in a partially open position disposed within a passage 204. FIG. 10 is a cross section of circular valve from FIG. 9 taken along the section line 10—10. The circular rotary valve 206 includes a valve stem 202 rotatable along an axis 200. By rotating the valve stem 202 along the axis 200, in the direction indicated by an arrow 211, the circular disc 203 comes into contact with a circular valve seal 209 to close off a passage 204. A wear area 205 (FIG. 10), located proximate to the axis 200 of the valve stem 202, is in continual engagement with the circular valve seal 209 as the circular disc 203 rotates in relation to the circular valve seal 209. As a result of continual engagement between the circular disc 203 and the circular valve seal 209, wear occurs either on the disc 203 or on the circular valve seal 209 at the wear area 205 adjacent to valve stem 202. As the distance d between the circular disc 203 and the centerline of the valve seal 209 decreases, the wear area 205 between the circular disc 203 and the circular valve seal 209 increases, thereby increasing the total associated wear. Stated another way, the prior art rotary valve 206 when utilized for actively throttling fluid flow to provide a small percentage of total flow capacity, incurs significant wear as a result of the wiping motion of the circular disc 203 relative to the circular valve seal 209. The presence of abrasive particulates suspended within the fluid may accelerate the wear experienced by the valve seal 209 and disc 203 at the contact area 205.
The wear inherent to this type of circular disc/seal interface often results in reduced seal integrity leading to an inability to completely retard the fluid flow through the rotary valve. The loss of accurate fluid flow control attributable to worn seals may cost a manufacturer substantial sums of money in either lost process control or valve services. As a result, a worn valve must be either repaired or replaced which may cost hundreds of thousands of dollars in material and/or process downtime. For example, shutting down a nuclear reactor to replace a valve or replacing a ruined batch of pharmaceutical product caused by a malfunctioning control valve, can result in significant losses due to lost productivity or product.
Another problem associated with by the prior art rotary valves is overcoming the “break away” friction of the valve, i.e. overcoming the static friction of the ball or disc required to open, close, or adjust the valve. Typically “high performance” rotary valves, which generally have a large break away friction, require a large initial force to overcome the static friction which can cause valve positioning instability because the large initial force is considerably greater than the force required to overcome the dynamic friction and hence an actuator will likely overshoot the desired setting. It would therefore be desirable to provide a “frictionless” rotary valve that would solve such valve control problems.
Another problem associated with the prior art rotary valves is the complicated centering and adjustment procedures required to position the disc relative to the valve seal. Because the periphery of the disc is used as the seal contact surface for the valve, it is critical to proper seal performance that the disc be precisely centered within the valve body. Numerous structures have been incorporated into the prior art rotary valve assemblies to address this problem and permit the installed disc to be adjusted within the valve body in a manner effecting this necessary disc centering. This centering adjustment, of course, must be carefully and accurately performed to achieve the desired sealing effectiveness. Adjustment error, on the other hand, can seriously reduce the valve's sealing efficiency.
Another problem associated with the prior art rotary valves is the complicated manner in which an actuator, a motorized device used to rotate the disc between its open and closed positions, is operatively mounted on the valve body. Typical rotary valves include an actuator base structure integrally formed or joined to the valve body and projecting radially outwardly from the valve body. An adaptor structure affixed to the outwardly projecting base structure provides a platform for mounting the actuator to the valve body. This complex mounting and adaptor structure undesirably adds to the overall manufacturing cost and complexity of assembly of the prior art rotary valve.
As highlighted by the foregoing discussion, a need exists for an improved rotary valve assembly, and the fabrication methods associated therewith, to eliminate or substantially reduce the above-mentioned problems, limitations, and disadvantages typically associated with rotary valves of conventional construction. It is desirable to provide a rotary valve having an effective mechanism for providing extended service life. It is a further desirable to reduce the wear between the disc and the sealing surface of the valve over a relatively large range of rotational distances. It is further desirable to provide a rotary valve having enhanced controllability, and substantially no seal engagement and wear until the disc provides substantial closure of the valve passageway, and to provide a simplified mechanism for the mounting of actuators to a valve body.